<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>多重边框</title>
  <style>

    /* 使用 box-shadow 创建出多边框效果*/
    .div1 {
      width: 300px;
      height: 300px;
      margin: 200px auto;
      background: yellowgreen;
      border-radius: 10px;

      /* x,y 偏移为0, 虚化半径为0, 扩散半径为边框宽度 */
      box-shadow: 0 0 0px 10px #655, 0 0 0px 20px darkorchid;
    }
    
    /* border 加 outline 创建多边框效果 */
    .div2 {
      width: 300px;
      height: 300px;
      margin: 200px auto;
      background: orange;
      border-radius: 10px;
      border: 10px dashed #655;
      outline: 10px solid deeppink;
      background-clip: padding-box;
    }

    /* border 加 outline 创建多边框效果 */
    .div3 {
      width: 300px;
      height: 300px;
      margin: 200px auto;
      background: orange;
      border-radius: 10px;
      box-shadow: 0 0 0 20px green;
      outline: 10px solid deeppink;
      /* background-clip: padding-box; */
    }
  </style>
</head>

<body>
  <div class="div1">
  </div>
  <div class="div2">
  </div>
  <div class="div3">
  </div>
</body>

</html>